Optoelectronic component and method for the production thereof

ABSTRACT

To secure an optical lens over an optoelectronic transmitter or receiver, it is proposed to use a UV-initiated or photoinitiated, cationically curing epoxy resin, by means of which the bonded joint can be set and thereby fixed in a few seconds. Also proposed, for use as adhesives, are resin compositions that can be applied as liquids, are optically matched, and are optimized for durable, reliable use in optoelectronic components and for the large-scale manufacture thereof.

[0001] The invention concerns an optoelectronic component comprising asupport body on which an optoelectronic transmitter or receiver isarranged, comprising a transparent layer placed over and encapsulatingthe transmitter or receiver, and comprising an optical element arrangedover the transparent layer.

[0002] Such a component is known, for example, from DE 19755734 Al.Described therein is an SMD-mountable optoelectronic component assembledon a support body provided with a recess. The optoelectronic transmitteror receiver is arranged in the recess and encapsulated with an opticallymatched transparent plastic layer. Arranged over the transparent plasticlayer and in direct contact therewith is a lens, serving as the opticalelement, by means of which the incidence of light on or radiation oflight from the component is controlled. A transparent casting compoundis used for the plastic layer, the lens being placed on the plasticlayer before said casting compound has cured completely. Curing of thecasting compound results both in good optical contact and in a good bondbetween the plastic layer and the optical lens.

[0003] This approach has the disadvantages that precise orientation ofthe lens is difficult and the lens has to be fixed relative to the basebody or support body during cure. Since this fixation must be maintainedfor the entire curing time, which, depending on the plastic used, can beup to several minutes and hours [sic], this complicates the productionof the optoelectronic component.

[0004] The object of the present invention is, therefore, to provide anoptoelectronic component in which an optical element such as a lens, forexample, can be oriented and fixed simply and reliably.

[0005] This object is achieved according to the invention by means of acomponent of the type cited at the beginning hereof, with the aid of thefeatures of claim 1. Advantageous embodiments of the invention and amethod for achieving precision-fit bonding will emerge from additionalclaims.

[0006] The invention proposes bonding the optical element to atransparent layer by means of an adhesive layer composed of asingle-component resin. By means of the invention, the plastic layerused as the transparent layer can be cured, and, optionally, its surfacetreated, independently of the optical element. The single-componentresin of the adhesive layer enables the optical element to be mounted onthe transparent layer in a simple manner.

[0007] A UV-initiated or photoinitiated, cationically cured epoxy resinis preferably used as the adhesive layer. Resins with this curingmechanism have the advantage that in a rapid photoinitiated orUV-initiated process, they pass into a gel phase that in itself issufficient for prefixation. Using such a resin as an adhesive thereforepermits rapid fixation of the parts to be bonded. Complete cure of theprefixed parts can then take place in a further step without the needfor any additional remedial measures such as fixations.

[0008] Under these circumstances, curing can take place in a fewseconds. It is even feasible to use only a flash of light or ultravioletto initiate cure. This is sufficient to fix the to-be-bonded parts sofirmly that their mutual orientation is maintained during completecuring, which can take place at an arbitrary later time. Rapid and exactfixation of the parts to be bonded is therefore feasible, which isespecially important in the case of optical systems.

[0009] The rapid setting of cationically curing resin has the furtheradvantage that is can be carried out at any desired temperature, whichcan be selected with a view toward the subsequent use of the bondedassembly and, in particular, the subsequent operating temperature of theoptoelectronic component. The preferred approach is to perform theradiation-induced preset of the adhesive layer at the lowest possibletemperatures, particularly at temperatures of 60° C. or less. Thisprevents any thermal stresses that might be induced in the bonded jointby thermal expansion during curing at high temperatures. A low-stressbond is also more stable and can be made in a reproducible manner. Anymaterial properties that may depend on the existing thermomechanicalload can therefore be adjusted constantly and reproducibly. Thisapproach also allows the complete cure to be performed at any later timethat may be desired.

[0010] The chemical and geometric structure of the adhesive layer isalso selected so that, under the temperature, moisture and radiationloads that have to be given greater consideration in the case ofoptoelectronic components, the adhesive layer will neither yellow norbecome cloudy, nor will its mechanical and mechanical [sic] propertiesdeteriorate. This also ensures that there will be no decrease inluminous efficiency or change in the radiation characteristic. Inaddition, the mechanical strength of the adhesive layer is not decreasedin response to said loads. Thus, the operating ability is certain tolast for the duration of production, qualification, and the ten years ofoperating time or service life that is standard for LEDs. The adhesivelayer and thus the optoelectronic component or LED are able to meet theexacting qualification requirements of the automotive industry.

[0011] Through suitable choice of the resin components, it is alsofeasible to obtain a resin with a sufficiently high glass transitiontemperature T_(G) of, for example, 120° C. or more. This ensures that acomponent bonded with this resin will function reliably at operatingtemperatures below the glass transition temperature. This high T_(G)also persists over the service life of the component, without decreasingunder temperature, light or moisture loading.

[0012] Once the resin has cured completely, it exhibits no opticalinhomogeneities of any kind, neither air inclusions nor cracks, tears ordelamination of any kind. The adhesive and thus also the adhesive bondis sufficiently temperature-stable and withstands the solder-bathconditions required for SMD assembly of the SMD component withoutincurring any damage or tendency to malfunction.

[0013] The cured adhesive layer can be adjusted to an index ofrefraction n_(D) of more than 1.50. It is thus ideally matched opticallyto the optical molding materials that are preferably used for theoptical element.

[0014] In the bonding of transparent parts, as in the case of thepresent invention, irradiation with UV or visible light that passesthrough the parts to be bonded results in exposure of the entire volumeof the adhesive layer, and setting/cure is therefore initiated uniformlythroughout. This can be achieved even at very low irradiances of lessthan 100 mW/cm².

[0015] The resin can be matched rheologically so as to permitmicrometering at 60° C. with a metering tolerance of <±3%, enabling theadhesive layer to be applied exactly and reproducibly in a thin layerthickness of, for example, up to 100 μm, with good adhesive propertiesfor the adhesive bond. The bonding process is laid out so that it can beperformed with high throughputs in large-scale, highly automatedproduction. This is achieved in particular by means of the fast settingtimes with which the lens becomes fixed to the plastic layer.

[0016] For the component according to the invention, it is preferable touse an epoxy resin system that can be applied as a liquid and that canhave the following general composition, stated in weight-percent: Bi-and multifunctional epoxy resin 80-99% Monofunctional epoxy resin(reactive diluent, 0-10% monoglycidyl ether) (Poly-)vinyl ether 0-20%Aliphatic or cycloaliphatic alcohol 0-10% Bonding agent(organofunctional alkoxysilane) 0-5% Flow agent, preferably silicon- oracrylate-based 0-1% Deaerator, preferably silicon- or acrylate-based0-1% Catalyst for UV-initiated cationic curing 0.1-2%

[0017] The photoinitiator used for the cationic cure can be, forexample, UV16974 (CIBA SC). For the subsequent thermal cure, additionalinitiators can be used to effect a cationically initiated thermal cure.Halonium and onium salts of sulfur (sulfonium salts) are preferably usedfor this purpose. A suitable thermal initiator is, for example,S-benzylthiolanium hexafluoroantimonate (Aldrich).

[0018] The invention will now be described in more detail with referenceto exemplary embodiments in combination with FIGS. 1 and 2.

[0019] In the drawing:

[0020]FIG. 1 is a schematic cross-sectional representation of a firstexemplary embodiment of a component according to the invention, and

[0021]FIGS. 2a and 2 b are, respectively, a schematic cross-sectionalrepresentation and a detailed view of a second exemplary embodiment of acomponent according to the invention.

[0022] Like or like-acting elements have been assigned the samereference numerals in the figures.

[0023] The base body for the component depicted in FIG. 1 is formed byextrusion-layer a conductive strip 2 with a high-temperaturethermoplastic, shaping a package 3 therefrom. The package has at itscenter a recess, in which the optical transmitter or receiver isarranged and is connected electrically to the conductive strip fromwhich the SMD-capable contacts are fabricated. The recess in the packagepreferably has inclined lateral faces 4 that can therefore serve asreflectors for the optoelectronic component.

[0024] After the optical transmitter or receiver 1 has been mounted andcontacted in the recess, the latter is filled with a flowable castingcompound, which is then cured to yield a plastic layer 5 thatencapsulates the transmitter or receiver. A thin layer 6 of aUV-initiated, cationically curing epoxy resin is then applied to theplastic layer 5 in a layer thickness of, for example, 90 μm. Placed onthis resin layer 6, which forms the subsequent bonding layer, is theoptical lens 7, as the optical element, which is oriented and isoptionally fixed briefly in its exact position.

[0025] The joint surface of the optical element is preferably providedwith structures 8 to improve the mechanical keying of the surfaces to bebonded. These can, for example, be lugs, nubs or similarly shapedprojections or indentations. A topology that is sawtooth-like in crosssection is also feasible. Such structures can be shaped on the jointsurface, for example.

[0026] In addition, the lens, or, generally, the optical element, canhave on its joint side a surface topology (not shown) that deviates fromthe planar. In particular, this can be a defined roughness or waviness.

[0027] In order to orient the to-be-bonded parts in an exact andreproducible spacing from one another, it is advantageous to disposespacing elements or spacers between the joint surfaces. These can bepart of one of the joint surfaces and can, for example, be formed on theoptical element.

[0028] To enable the radiation characteristic to be adjusted to specificneeds, the lens itself can have not only the convex geometry shown, butalso a planarly parallel or a concave incident surface and various radiiof curvature.

[0029] After the optical element has been oriented, the entirearrangement is exposed briefly from above to UV radiation, for example aUV flash. After a few seconds, particularly after a period of 0.1 to 5seconds, the optical lens 7 is sufficiently fixed on the plastic layer 5and the adhesive layer 6 is sufficiently set.

[0030] In a second step, the adhesive layer 6 is then cured completely,for example for two hours at a temperature of 120° C.

[0031] The following compositions, stated in parts by weight (pbw), areselected for the UV-initiated, cationically cured epoxy resin usedaccording to the invention.

EXAMPLE a)

[0032] Bisphenol A epoxy cast resin GY260 88.9 pbw Epoxynovolak D.E.N.438 10.9 pbw Tego-DF48 (a bonding agent)  0.4 pbw Initiator UVI6974  1.0pbw

EXAMPLE b)

[0033] Bisphenol A epoxy cast resin GY260 88.9 pbw Epoxynovolak D.E.N.438 10.0 pbw BYKA506  0.4 pbw Initiator UVI6974  0.7 pbw

[0034] The optoelectronic components obtained with both epoxy resincompositions, a and b, have adhesive layers that are so stable againsttemperature, moisture and radiation loading under the potentialoperating conditions of the component that they do not exhibit eitheryellowing, clouding or any other change that might decrease luminousefficiency or alter the radiation characteristic. The resin compositionsare able to set in a few seconds and demonstrate sufficient bondingstrength after complete cure. They survive solder-bath conditions of3×260° C. without damage and with no reduction of the thermomechanicalproperties of the adhesive layer.

[0035] A further modification, not described in the exemplaryembodiments, concerns the addition of a given quantity of vinyl ethersto further shorten the setting time. This expedites the setting processand thus further increases throughput in the production of theoptoelectronic components. In addition, the other ingredients can beselected for ideal optical matching to the plastic layer, thuseliminating the disadvantage of optical losses at the transition fromthe plastic layer to the adhesive layer or the transition from theadhesive layer to the lens.

[0036] A further exemplary embodiment of a component according to theinvention is depicted schematically in cross section in FIG. 2.

[0037] In contrast to the first exemplary embodiment, here the lens 7has on its joint side an obliquity 9, so that the bond gap widens towardthe edge of the component. This obliquity 9 can also, for example, beimplemented as a circumferential bevel on the joint side of the opticalelement.

[0038] This shaping creates a reservoir for excess adhesive. Due tosurface tension, at its edge the adhesive forms a fillet 10, as shownmore closely in the detailed view of FIG. 2b. This advantageouslyreduces the risk that excess adhesive will reach the side walls of thepackage. It also reduces requirements in terms of the metering accuracyof the adhesive.

[0039] Formed on the joint surface of the optical element are lug-likestructures 8 that serve as spacers between lens 7 and plastic layer 5.This ensures a defined and consistent thickness for the adhesive layer6. At the same time, these spacers 8 constitute a keying between theadhesive layer 6 and the lens, which increases the strength of theadhesive bond.

[0040] The explanation of the invention with reference to the describedexemplary embodiments is, of course, not to be construed as limiting theinvention thereto.

1. An optoelectronic component comprising a support body on which anoptoelectronic transmitter or receiver is arranged, comprising atransparent layer placed over and encapsulating said transmitter orreceiver, comprising an optical element arranged over said transparentlayer, characterized in that said optical element is bonded to saidtransparent layer by means of an adhesive layer composed of asingle-component resin.
 2. The component as recited in claim 1, whereinsaid adhesive layer is a UV-initiated or photoinitiated, cationicallycured epoxy resin.
 3. The component as recited in claim 1 or 2, whereinsaid adhesive layer has a glass transition temperature of more than 100°C.
 4. The component as recited in any of claims 1 to 3, comprising anadhesive layer that is optically matched to said transparent layer. 5.The component as recited in any of claims 1 to 4, wherein saidtransparent layer and said optical element are made of glass, ofpolyacrylate, of polyurethane, or of epoxy resin molding compound. 6.The component as recited in any of claims 1 to 5, wherein said opticalelement has a defined roughness or waviness on its joint surface.
 7. Thecomponent as recited in any of claims 1 to 6, wherein a keying isrealized on the joint side of said optical component.
 8. The componentas recited in claim 7, wherein said keying is realized by means ofindentations or projections, particularly in the form of nub- orlug-like structures formed on said optical element.
 9. The component asrecited in claims 1 to 8, wherein spacing elements are arranged betweensaid optical element and said transparent layer and are preferablyformed on said optical element.
 10. A method for the precision-fitbonding of transparent parts of optoelectronic components, comprisingthe steps of: applying a thin resin layer of a cationically initiated,curable epoxy resin to one surface of one of the transparent parts to bebonded, placing and orienting a further transparent part on said resinlayer, exposing the assembly to UV or visible radiation in order to setsaid resin layer, curing said resin layer completely.
 11. The method asrecited in claim 10, wherein the complete cure of said resin layer isperformed at elevated temperature.
 12. The method as recited in claim 10or 11, wherein the exposure to UV radiation is effected for less than 5s at an irradiance of less than 100 mW/cm².
 13. The method as recited inclaim 12, wherein said exposure to UV radiation is effected by means ofa UV flash and curing is performed at temperatures above 120° C.
 14. Themethod as recited in any of claims 10 to 13, wherein an epoxy resincomprising a diglycidyl ether of bisphenol A as its chief constituentand a cation-releasing photoinitiator is used for the resin layer. 15.The method as recited in claim 14, wherein an epoxy resin is used thatincludes the following constituents, stated in weight-percent: 80 to 99%bi- and multifunctional epoxy resins 0 to 10% monofunctional epoxy resin0-19% vinyl ether 0-10% aliphatic or cycloaliphatic alcohol 0-5% bondingagent 0.1-5% photoinitiator for cationically initiated curing.
 16. Theuse of a cationically initiated, curable epoxy resin having a diglycidylether of bisphenol A as its chief constituent for the positionallyprecise bonding of transparent parts of optoelectronic components toadditional optical elements such as mirrors or lenses.
 17. The use asrecited in claim 16 for reliably bonding the following combinations ofmaterials constituting parts to be joined: plastic/plastic,plastic/glass, glass/glass.
 18. The use as recited in claim 17 for thefunctionally reliable bonding of SMD-capable optoelectronic componentsfor the automotive industry.